Originally Posted by
dwood
P the G,
The 'heat' method is only effective on metals with different expansion rates: e.g. aluminum and steel. The broken allen wrench and the bolt are both steel.
If you have a dremel tool you should be able to take a pointed carbide cutter and work it gently around the hex cavity in the bolt head . . . tapering it [bell-mouthing it]. eventually you will have enlarged it enough to let the broken wrench piece fall out.
There should be enough of the original socket in the bolt to use a standard allen wrench in it and remove the bolt. Replace the bolt with a new one.
Thanks, dwood, for saving me some wasted time with the heat method. I'll give the carbide cutter a go tomorrow, but is there much danger of damaging the hex cavity enough that I will no longer be able to use a hex wrench to remove the bolt?